Most computing devices employ some type of authentication to confirm that a user of the device is who he or she claims to be and to prove that the user is authorized to access the device. Authentication is necessary to prevent an unauthorized user from accessing an unattended computing device. Typically, authentication is based on a username and a password. Other forms of authentication may require a user to draw patterns on a screen or to input a secure code. These authentication processes may not be fully secure because unscrupulous passersby may observe the user performing the authentication and later repeat the process on the user's computing device. In addition, typical authentication may be time consuming, especially since a user of a mobile computing device may want to quickly access the device to make an urgent phone call. Authentication may be more secure using a one-time password that is valid for one login session or transaction. However, one-time passwords are not convenient because the user is required to carry around a token that generates the password, and the password must be entered into the computing device.